By Harkirat Kaur and Maninder Singh et.al
Infections by fungi such as Aspergillus, Fusarium, Penicillium and Gibberella spp. in corn can cause accumulation of mycotoxins (toxic secondary metabolites) in plant biomass. This accumulation can deteriorate corn silage quality. Cool and wet weather conditions around silking of corn silage tends to be very favorable for growth of Fusarium graminearum and may cause high deoxynivalenol (DON, or vomitoxin) accumulation. Feeding by birds, animals and ear damaging insects such as western bean cutworm and European corn borer can provide easy entry to the fungus and intensify infections.
Some mycotoxins, especially DON, zearalenone (ZON) and fumonisins, can cause feed rejections leading to loss in milk production, hormonal imbalance, reduced reproductive performance and in some cases the death of animals. They can have serious economic consequences on farms if present in sufficient concentrations. Very often, various mycotoxins coexist in silage and their impacts on the health of livestock may be synergistic. This makes it difficult to determine safe levels (thresholds) for individual mycotoxins.
To understand the extent and gravity of the mycotoxin issue, the Michigan State University Cropping System Agronomy lab initiated a survey of Michigan corn silage in 2019 for analysis of 26 mycotoxins. These efforts were repeated in 2020 to gather more samples and data. A total of 49 samples from across 20 counties during harvesting season 2020 and 34 samples from 11 counties in 2019 were collected for analysis.
Results from 2020 showed that all samples tested positive for at least one mycotoxin. Deoxynivalenol was found to be positive in all 49 samples. This was similar to 2019 also, when all samples tested positive for DON. At least 12% of the samples had DON concentrations higher than 1 ppm (DON threshold limit) in 2020 whereas in 2019 about 50% of samples had DON levels higher than 1 ppm. Other mycotoxins that occurred in all samples were enniatins and beauvericin, but their concentrations were low. However, when present in high concentration, beauvericin and enniatins can negatively impact androgen receptors and can also impede muscle contraction in cattle.
The second most frequently occurring category of mycotoxins found were fumonisins—47 out of 49 samples tested positive with eight samples having levels higher than threshold (2 ppm). Fumonisin levels were as high as 10 ppm in two samples. Mycotoxins were found to co-exist in most of the silage samples. Four samples tested positive for more than 20 mycotoxins. Each sample tested positive for at least seven different mycotoxins.
Overall, since the 2020 growing season was drier and rainfall was more sporadic, mycotoxins occurred in lower concentration and frequency than the previous year. The mycotoxin co-existence was also more pronounced in 2019 than in 2020 with a maximum of 24 mycotoxins detected in a single sample. Also, the highest DON and ZON concentrations were 5.7 and 2.5 ppm in 2019, respectively, while in 2020 highest toxin concentrations were 1.4 ppm for DON and only 0.07 ppm for ZON. The only toxin that occurred in higher concentration in 2020 than in 2019 was fumonisin (highest concentration reported 10.6 ppm in 2020). This is because fumonisin accumulation occurs due to F. verticilloides infection, which is favored when the environment is warm and dry around silking.
Results from 2019 and 2020 showed that mycotoxins are present in Michigan silage and their frequency and concentration largely depend on the temperature and moisture conditions throughout the growing season and, in particular, around silking. Since there are few ways to overcome problems once mycotoxins are present in corn, prevention of mycotoxin accumulation in the field is essential. Field management strategies begin with crop rotation and hybrid selection (including insect protection traits), scouting and spraying for ear feeding insects, fungicide application and harvest timing (early harvest can help in preventing toxin accumulation later in the season). Hybrid selection and insect control help control ear rot infections and eventually mycotoxin accumulation.
Furthermore, hybrids with resistance against stalk rots can also help alleviate the accumulation of mycotoxins. Research shows a significant amount of mycotoxins are contributed by stalk rots as well. Fermentation processes in bunker silos will not break down mycotoxins from an already infected silage which makes the field management even more crucial.
We are continuing our efforts to determine the effects of management practices, insect damage and weather conditions on mycotoxin development in corn silage. Please visit our Cropping Systems Agronomy website for more details.
Farmers are invited again to submit corn silage samples for free testing of 26 different mycotoxins and quality analysis. Silage samples of approximately 1 pound should be collected from various locations in the same field and then either dried or frozen soon after collection. A data sheet along with sample collection instructions is available and can be used to record detailed field information and sent along with samples. This information must be completed before samples will be analyzed. Results will be available the following summer as individual grower reports.
Continued participation by corn silage producing farmers in this study will enable Michigan State University researchers and Extension educators to better help farmers improve control of mycotoxins and, therefore, improve cattle performance.
Source : msu.edu